This proposal is divided into three sections, each with a separate, specific objective. The first section is directed toward developing new surgical techniques that will preclude the necessity for implanting artificial pacemaking systems in patients who presently require His Bundle ablation for the treatment of refractory supraventricular tachycardia. In addition, surgical techniques are proposed that may ablate the detrimental effects of chronic atrial fibrillation associated with mitral valve disease. The second section of the proposed involves the surgical treatment of ventricular tachyarrhythmias associated with ischemic heart disease and has three major objectives: 1) clarification of the electrophysiologic mechanism whereby left ventricular endocardial surgical techniques ablate ischemic ventricular arrhythmias, 2) the effect of these surgical procedures on regional myocardial function, regional myocardial blood flow, and left ventricular structural integrity, and 3) development of a safe and effective surgical technique for the treatment of ischemic ventricular dysrhythmias based upon evolving concepts of the pathogenesis of these dysrhythmias. The third section of the proposal is designed to establish a method whereby myocardial integrity can be monitored quantitatively on a continuous basis during and after cardiac surgical procedures. The method depends upon differentiation between the electrophysiologic indices of reversible and irreversible myocardial ischemic injury. These electrophysiologic indices will be used to determine the adequacy of myocardial preservation during cardiopulmonary bypass and to detect myocardial ischemic injury sufficiently early to allow therapeutic intervention to prevent permanent myocardial damage.